There are three major objectives of the proposed conference: Goal One. Dissemination, to a wide range of professionals concerned with diagnosis and remediation of developmental disorders of childhood, of the results of the initial four years of an eight year longitudinal classification study (NS20489, Nosology: Higher Cerebral Function Disorders in Children) of 256 preschool children with developmental language disorders (DLD) and 191 with autistic spectrum disorders (ASD). The children were selected and studied systematically with medical, neuropsychologic, language, play, neuroimaging and electro-physiologic measures. Two key issues will be addressed: (1) what are the early precursors of learning disabilities? and (2) what are the range, nature, and boundaries of subgroups of developmentally handicapped children? Goal Two. Formal evaluation of problems with sample selection and classification such as: (a) Traditionally used criteria for identifying children as "developmentally language disordered" were shown to capture little more than half of all children who had deficits in spontaneous language and who were designated as having language disorders by trained clinicians. (b) Play and sociability data helped clarify fuzzy boundaries between high functioning children who met diagnostic criteria for ASD and children with DLD whose social skills were somewhat compromised. (c) Medical histories and formal neurologic examinations did not lead to better groupings or clarify individual profiles of children. Goal Three. Generation of ideas and concrete plans for future interdisciplinary research. Invited discussants will present formal critiques of the data reported by the members of the research team, focusing on unanswered questions and new methodologies to address them.